Hagia Sophia, (the Church of) Holy Wisdom, now known as the Ayasofya Museum, is a former Eastern Orthodox church converted to a mosque in 1453 by the Turks, and converted into a museum in 1935. It is located in Istanbul, Turkey. It is traditionally considered one of the great buildings in history. Its conquest by the Ottomans at the fall of Constantinople is considered one of the great tragedies of Christianity by the Greek Orthodox faithful.

The name comes from the Greek name Ἁγία Σοφία, a contraction of Ναός τῆς Ἁγίας τοῦ Θεοῦ Σοφίας, meaning “Church of the Holy Wisdom of God”. It is also known as Sancta Sophia in Latin and Ayasofya in Turkish. Although it is sometimes called “Saint Sophia” in English, it is not named after a saint named Sophia — the Greek word sofia means “wisdom.”

Hagia Sophia is covered by a central dome with a diameter of 31 meters (102 feet) and 56 meters high, slightly smaller than the Pantheon’s. The dome seems rendered weightless by the unbroken arcade of arched windows under it, which help flood the colorful interior with light.

The dome is carried on pendentives — four concave triangular sections of masonry which solve the problem of setting the circular base of a dome on a rectangular base. At Hagia Sophia the weight of the dome passes through the pendentives to four massive piers at the corners. Between them the dome seems to float upon four great arches.

At the western (entrance) and eastern (liturgical) ends, the arched openings are extended by half domes carried on smaller semidomed exedras. Thus a hierarchy of dome-headed elements builds up to create a vast oblong interior crowned by the main dome, a sequence unexampled in antiquity. All interior surfaces are sheathed with polychrome marbles, green and white with purple porphyry and gold mosaics, encrusted upon the brick. On the exterior, simple stuccoed walls reveal the clarity of massed vaults and domes.

Nothing remains of the first church that was built on the same site during the 4th century. Following the destruction of the first church, a second was built by Constantius II, the son of Constantine I, but was burned down during the Nika riots of 532. The building was rebuilt under the personal supervision of Emperor Justinian I and rededicated on December 27, 537. After the great earthquake in 989, which ruined the dome of St Sophia, the Byzantine government sent for the Armenian architect Tirdat, creator of the great churches of Ani and Agine, to repair the dome.[1] Justinian chose Isidore of Miletus and Anthemius of Tralles, a physicist and a mathematician, as architects; Anthemius, however, died within the first year. The construction is described in Procopius’ On Buildings (De Aedificiis). The Byzantine poet Paulus the Silentiary composed an extant poetic ekphrasis, probably for the rededication of 563, which followed the collapse of the main dome.

Hagia Sophia is one of the greatest surviving examples of Byzantine architecture. Of great artistic value was its decorated interior with mosaics and marble pillars and coverings. The temple itself was so richly and artistically decorated that Justinian proclaimed “Solomon, I have surpassed thee!” (Νενίκηκά σε Σολομών). Justinian himself had overseen the completion of the greatest cathedral ever built up to that time, and it was to remain the largest cathedral for 1,000 years up until the completion of the cathedral in Seville.

I think this is an accurate image of the interior of Hagia Sofia. It captures the gloomy darkness of the enormous space. This is an interior view from the gallery, which is really wide (huge) and goes all the way round the building. You reach it by an enormous stone ramp made of large uneven boulders, rather than steps. This astonishing Byzantine building blows my mind. It is genuinely one of the wonders of the world. Following the destruction of the two previous churches on the site, the building that you see now was rebuilt under the personal supervision of emperor Justinian I and rededicated on December 27, 537ad. That makes it 1500 years old! It was the largest cathedral ever built for over 1,000 years and today is still the fourth largest cathedral in the world.